Micro-miniature relay



3937 R. L. MARTIN 3,335,376

MICRO -MINIATURE RELAY Filed Dec. 13, 1965 2 Sheets-Sheet 1 505w) L. Mar/1h,

INVENTOR.

J/forney:

Aug. 3, 19%? MARTIN I 3,335,375

MICRO -MINIATURE RELAY Filed Dec. 1-3, 1965 2 Sheets-Sheet 2 Faber) L Mar/l INVENTOR.

l/larnays BY Beak/er f iron/ United States Patent 3,335,376 MICRO-MINIATURE RELAY Robert L. Martin, La Canada, Calif, assignor to Charles E. Gutentag P.B.A. Publication Engineers, Los Angeles, Calif.

Filed Dec. 13, 1965, Ser. No. 513,908 6 Claims. (Cl. 335-125) The invention has reference to micro-miniature electrical equipment and is specially concerned with a microminiature relay. Although the size is variable as to different conditions, a typical and frequent embodiment is one contained in a housing about inch in diameter and about of an inch long.

The design of micro-miniature equipment has advanced very remarkably in recent years with the calls upon it placed by missile and space vehicle demands. Although technology has evolved many successful micro-miniature relays and switches with acceptable performance characteristics, there are still additional shortcomings to be overcome. One of these is the high cost of dependable devices, made necessary by the need for extreme care in assembling numerous intricate parts and the waste involved in rejecting completed devices which do not satisfy tests for dependability. Moreover, in micro-miniature devices, wherein the operating cycle is extremely high, such devices lack a desirable life span and frequently need removal and replacement in order to keep a piece of equipment operating properly and dependably. The very limited clearances which have to be built into such a device, separating moving operating parts, places considerable dif ficulties in the path of fabrication and assembly of such devices in appreciable quantities.

It is, therefore, among the objects of the invention to provide a new and improved micro-miniature relay device of such construction that very narrow clearances between moving operating parts can be assured by reason of the inherent construction of the device.

Another object of the invention is to provide a new and improved micro-miniature relay device wherein the structure and arrangement of parts is such that they can be rapidly and dependably assembled by employment of suitable jigs so that uniformity can be preserved even when such devices are produced in quantity.

Another object of the invention is to provide a new and improved micro-miniature relay device, certain portions of which can be prepared as sub-assemblies for ease of access to critical portions of the device and thereafter quickly and dependably assembled together in a fashion assuring reliable performance.

Still another object of the invention is to provide a new and improved micro-miniature relay device wherein the number of separate parts is held to substantially a minimum and wherein by reason of the sub-assembly technique of construction the cost of the finished article is appreciably lower without in any way sacrificing its reliability.

Still further among the objects of the invention is to provide a new and improved micro-miniature switch or relay mechanism capable of being produced in a size appreciably smaller than many comparable devices, while at the same time holding costs to a very nominal figure and increasing the operating life span for dependable operation far beyond most devices currently available.

Also included among the objects of the invention is to provide a new and improved transient voltage suppression micro-miniature relay device which makes use of portions of the customary construction, but wherein material of different magnetic and electrically conducting characteristics is employed.

Still further among the objects of the invention is to 3,335,376 Patented Aug. 8, 1967 provide a new and improved micro-miniature relay device which is rendered particularly capable of suppressing transient voltages by means of a specially constructed and applied non-magnetic jacket of such character that there is, for all practical purposes, no appreciable change in the overall size of the device.

With these and other objects in view, the invention consists in the construction, arrangement, and combination of the various parts of the device, whereby the objects contemplated are attained, as hereinafter set forth, pointed out in the appended claims and illustrated in the accompanying drawings.

In the drawings:

FIGURE 1 is a longitudinal sectional view of the device.

FIGURE 2 is a cross sectional view taken on the line 2-2 of FIGURE 1.

FIGURE 3 is a cross sectional view taken on the line 3-3 of FIGURE 1.

FIGURE 4 is a cross sectional view taken on the line 44 of FIGURE 1.

FIGURE 5 is a fragmentary longitudinal sectional view revealing certain critical phases of the construction.

FIGURE 6 is a side elevational view of the armature sub-assembly.

FIGURE 7 is a longitudinal sectional view of another form of the device, in which is incorporated transient voltage suppression structure.

FIGURE 8 is a cross sectional view taken on the line 8-8 of FIGURE 7.

In an embodiment of the invention chosen for the purpose of illustration, a housing 10 is shown having a closed end 11 and a side wall 12. The end opposite the closed end is adapted to be closed by employment of a glass seal disc 13 having a rim 14 adapted to be hermetically attached to an edge 15 of the side wall 12. The housing and the glass seal disc enclose a chamber 16 which is adapted to be evacuated through an evacuation and filling tube 17, an end 18 of which can be closed in the customary manner after the chamber 16 has been filled with an appropriate inert gas.

Generally speaking, the device may be considered as involving three sub-assemblies in addition to the housing 10. One sub-assembly identified as a header assembly, indicated by the reference character 20, consists of the glass seal disc 13 and the parts attached thereto. A sec- 0nd sub-assembly identified as a coil assembly 21, includes the electrical and magnetic portions of the coil and the structure upon which they are mounted. A third subassembly identified as an armature assembly 22 and shown separately in FIGURE 6, consists of an armature and its supporting parts, these being assembled separately prior to insertion within the coil assembly, after which both the coil assembly and the armature assembly are electrically connected to and physically mounted upon the header assembly 20.

Those elements included in the header assembly 20, not heretofore specifically referred to, consist of conducting pins for making electric contact with the relay device. The conducting pins 25, 26, and 27 interconnect with the switching portion of the device. Conducting pins 28 and 29 interconnect with the coil assembly. All of the pins 25, 26, 27, 28, and 29 are sealed in a fixed position in the glass seal disc 13.

The coil assembly is made up of a rear magnetic plate 30, a front magnetic plate 31, and a coil form 32 having one end 33 to which the rear magnetic plate 30 is attached and another end 34 to which the front magnetic plate 31 is attached. The space surrounding the coil form 32 and between the ends 33 and 34 is occupied by a magnetic coil 35. A magnetic sleeve 36 is applied over the magnetic coil 35 and extends between the rear magnetic plate 30 and the front magnetic plate 31. When direct current is passed through the magnetic coil, one magnetic plate becomes north pole and the other magnetic plate south pole, depending on the direction of flow of current.

The magnetic plates are substantially identical in form, although oriented in opposite directions. By way of example, the rear magnetic plate 30 has a horseshoe-like shape including an intermediate connecting portion 37 and opposite legs 38 and 39 forming a space 40 between the ends of the legs. Similarly, the front magnetic plate 31 has a connecting portion 41 and opposite legs 42 and 43 forming a space 44 therebetween. A bore 45 extends axially through the coil form 32 and connecting portions 37 and 41 of the respective magnetic plates partially overlie opposite ends of the bore.

Afiixed to the lower end of the coil assembly, as viewed in FIGURE 1, is a fixed contact insulator 46 of appropriate dielectric material. An appropriate adhesive may be employed for fastening the insulator in place. Covering the exterior of the magnetic coil is a layer of insulating tape 47 which extends from one end to the other.

In the fixed contact insulator 46 are two fixed contacts, namely a normally closed fixed contact 48 and a normally open fixed contact 49. These fixed contacts are anchored in position in appropriate respective recesses 50 and 51 by a suitable adhesive. A welding tab 52 interconnects the normally closed fixed contact 48 with the pin 25 and a welding tab 53 interconnects the normally open fixed contact 49 with the pin 26. An insulated welding tab 54 is attached to the pin 27 and connected in the insulator 46.

The armature assembly 22, illustrated as a separate sub-assembly in FIGURE 6, includes an armature bar 55 which, in the chosen embodiment, is square in cross sectional shape. The armature bar has a movable contact 56 welded on the right hand end, as viewed in FIGURE 6, and coined to give it a precise shape. The movable contact is preferably cylindrical in shape and presents a circular form in cross section. For mounting the armature bar 55 there is provided an armature mounting sleeve 57 and a pivot pin 58 extending in a transverse direction centrally between opposite ends of the armature bar 55 extends into appropriate openings 55 and 55" in the armature mounting sleeve 57 on diametrically opposite sides thereby providing a pivot support for the armature bar in the mounting sleeve.

An armature return spring 59 includes coils 60 and 61 on respectively opposite sides encircling opposite ends of the pivot pin 58. A saddle 62 interconnected with the coils 60 and 61, underlies the armature bar 55 at a location intermediate the pivot pin 58 and the movable contact 56. At least one leg 63 is made use of in the chosen embodiment and is shown extending toward the left from coil 60 in FIGURE '6. The leg 63 terminates in an outer end 64 which underlies an arm 65 forming part of a retaining tab 66. The retaining tab in turn is fixed to the armature mounting sleeve 57. The armature assembly, constituting the parts herein just described and shown in FIGURE 6, is adapted to be inserted in the bore 45 from one end, preferably the end of the bore to which the rear magnetic plate 30 would ultimately be attached. Once in position, the armature assembly is anchored in place by a spot of adhesive applied to the outer end 64 of the spring and the arm 65 fastening these two parts to the end 33 of the coil form.

A pigtail 67, forming a loop, has one end welded to the conducting pin 27 and the other end welded to the movable contact 56.

When the normally closed fixed contact 48 and the normally open fixed contact 49 are assembled to the fixed contact insulator 46 the tabs 52, 53, and 54 are located tangent to the edge of the conducting pins 25, 26, and 27, within the header assembly 20. The tabs 52, 53, and 54 form a triangular mechanical support for attaching the switching portion of the device to the header assembly 20. Lead wires 68 and 69 from the magnetic coil 35 are routed through appropriate slots 70 and 71 and welded to respective header conducting pins 28 and 29, thereby electrically connecting the coil 35 to the pins 28 and 29.

Preferably an assembly jig (not shown) is used to hold the header assembly 20 and the assembled switching components and established close concentricity and perpendicularity relationships so that the housing 10 and the side wall 12 thereof can be installed without interference and welded to the header assembly Zt'hvith hermetic seal integrity.

Critical dimensions are controlled by use of specially designed assembly jigs and fixtures. The spacing between the fixed contacts 48 and 49 attached to the fixed contact insulator 46 is held to a maximum variation of .0005 inch. The inside diameter of the coil form, namely the bore 45, is used as a reference for a suitable fixture to locate the front magnetic plate 31 and the normally open fixed contact 49 parallel to the axis of the bore 45. This is indicated by a surface 74, which is the exterior diameter of the movable contact 56.

A dimension 75, which is the space between the adjacent edge of the armature bar 55 and the face of the connecting portion 41 of the front magnetic plate 31, is held by proper location of the tangent surface of the movable contact 56 with respect to a flat side of the square armature bar 55, by coining the movable contact 56 in an appropriate die. The forming die, thus employed, controls a dimension 76 of the movable contact 56 at the same time the dimension 75 is maintained.

The control of critical dimensions in this way, prevents accumulation of dimensional tolerances when assembling the fixed contacts 48 and 49 and the movable contact 56, and minimizes operational dilferences between individual switching devices due to varying contact spacing. The bore 45 of the coil form also serves as a reference for the surface 74 as well as insuring accurate positioning of the armature assembly with respect to the other switch components.

After the armature assembly 22 has been inserted and properly positioned with respect to the remaining components, the armature bar 55 is held so that the movable contact 56 is forced against the fixed contact 48. The rear magnetic plate 30 is located with an appropriate fixture so that a dimension 77 establishes the minimum air gap at the rear of the armature to prevent the armature from striking the magnetic plate during normal operation of the switch.

The retaining tab 66 also serves as a clamp to hold the free end of the armature return spring. The free end of the spring is formed during final assembly to adjust spring load. When proper spring load is obtained, the free ends of the spring and tab are then cemented in place, as has been previously noted.

In operation, when the coil 35 is energized, the return spring 59 pivots the armature bar 55 about the pivot pin 58 so that the movable contact 56 is held against the fixed contact 48, thereby completing the electrical connection of the contacts 48 and 56. The coil 35 is then energized with a direct current, creating magnetic poles of opposite polarity at the ends of the armature bar 55. The armature bar is magnetically attracted to both the rear magnetic plate 30 and the front magnetic'plate 31. The magnetic attractions create a moment about the pivot pin 58 so that the movable contact 56 moves against the fixed contact 49, thereby completing the electrical connection between the contacts 56 and 49, and simultaneously opening the electrical conrrection between the contacts 48 and 56.

To further intensify the magnetic attraction of the armature bar 55 to the magnetic plates 30 and 31, the magnetic sleeve 36 is employed to complete the magnetic path at the exterior of the coil 35. When the coil simultaneously opening 35 is subsequently deenergized, the magnetic field collapses, eliminating the magnetic pull of the armature bar 55 to the magnetic plates 30 and 31. The force of the return spring 59 rotates the armature bar 55 about the pivot pin 58, forcing the movable contact 56 to move against the fixed contact 48, thereby completing the electrical connection between the contacts 56 and 48 and the electrical connection between the movable contact 56 and the fixed contact 49. the cycle is thus completed and the apparatus is ready immediately for the next succeeding cycle.

In the device, of the type here under consideration,

when used in certain environments there exists a likelihood of a transient electric condition, which is created momentarily when the relay coil is denergized and the electromagnetic field which has been operating collapses. This condition, frequently termed a voltage spike, can often be quite high, as much as 1000 volts or more on occasions. If this voltage spike is not suppressed, it can cause damage to or malfunctioning of associated components. Although some attempts have been made to correct this unwanted circumstance, such as for example, bifilar winding of the coil, such a remedy produces a coil of unwanted larger diameter and even though a successful supressant has both physical and electrical disadvantages, mechanical shielding, heretofore attempted, has been too bulky and uneconomical.

' In the form of device of FIGURES 7 and 8, a special shielding jacket has been made use of. A portion of the jacket consists of a relatively thin sleeve 78 of non-mag netic and relatively high conductive material. This sleeve is located between a magnetic sleeve 79 and a layer 80 of insulation around the magnetic coil 35. A good material for the sleeve 78 is silver and, for the micro-miniature device here under consideration, the thickness can be approximately .008 inch. This sleeve 78 extends inwardly so as to overlie outer edges of the front and rear magnetic pole plates 31 and 30.

Underlying the pole plates, respectively, are positioned suppression washers 81 and 82, likewise of nonmagnetic material and relatively thin, preferably the same material as the sleeve 78 and of about the same thickness. It will be noted that these washers 81 and 82 overlie respective ends 34 and 33 of the coil form.

To complete the jacket, the armature assembly in this instance, makes use of an armature mounting sleeve 83 likewise of non-magnetic material and preferably also of silver. The armature mounting sleeve 83, however, can be somewhat thicker and should extend for the full length of the bore 45. The balance of the armature assembly is like that already described 1 through 6, inclusive.

The items last described as consisting of non-magnetic relatively high conductive material, create shorted turns closely coupled to a large percentage of the flux linkages created by the electromagnetic coil and the path of the armature bar 55, the rear magnetic plate 30, the magnetic sleeve 79, and the front magnetic plate 31. The currents induced in the shorted turns s-ufficiently oping the magnitude of the transient voltage induced in the coil. The closed magnetic path closely couples the elements just made reference to, through the actuating coil of the relay.

Another approach to transient voltage suppression is to construct the coil form 32 with the ends 33 and 34 consisting of'a' highly conductive material, such as aluminum. Under such circumstances, it is necessary to provide adequate additional insulation between the magnetic coil 35 and all portions of the coil form to prevent voltage breakdown between the coil and the coil form. In this case, the coil form and its ends provide the conductive shorted turns which were described as supplied by the washers 81 and 82 in the form of device of FIGURES 7 and 8. The small diameter of the in connection with FIGURES magnetic pose transient changes in the coil current, thereby reduc-v 6 coil form provides the mounting for the armature mounting sleeve which should also be of silver, as described for the sleeve 78. In this last described approach, the sleeve 78 of non-magnetic highly conductive material, is also made use of in the same manner as has previously been described.

While theinvention has herein been shown and described in what is conceived to be the most practical and preferred embodiment, it is recognized that departures may be made therefrom within the scope of the invention, which is not to be limited to the details disclosed herein but is to be accorded the full scope of the claims so as to embrace any and all equivalent devices.

Having described the invention, what is claimed as new in support of Letters Patent is:

1. A micro-miniature electric relay device comprising a coil form having a bore therethrough, north pole and south pole plates at opposite ends of said coil form and a coil winding around said coil form intermediate said north pole and south pole plates, a pair of electric contacts having a fixed position relative to said coil form, and an armature sub-assembly comprising an armature bar of cross sectional shape smaller than said bore and having a length in excess of the distance between said pole plates, an armature mounting sleeve having an eX- terior circumference substantially the same as the interior circumference of said bore, a retaining tab secured at one end to the mounting sleeve, the other end of said tab having an arm adapted to overlie the coil form, means intermediate opposite ends of said bar pivotally mounting said bar in said mounting sleeve, an armature return spring having a saddle in engagement with said bar at one side of a pivot point and another portion at the end opposite said saddle having a retained position relative to said tab, a movable electric contact on said bar at a location between said pair of electric contacts and spaced from one of them, and a flexible connection from said movable electric contact, said armature mounting sleeve being slideable into said bore from one end whereby to mount said armature sub-assembly in operating position.

2. A micro-miniature electric relay device comprising header assembly having electric contact pins extending therethrough, a coil form having a bore therethrough, north pole and south pole plates at opposite ends of said coil form, and a coil winding around said coil form intermediate said north pole and south pole plates, a conductor insulator element having at least three combined mechanical and electrical connections to said header assembly forming-a supporting triangle, said insulator element having a fixed position relative to said housing at a location intermediate one of said pole plates and said header assembly, a pair of fixed electric contacts on said insulator element having a space therebetween and includingrespective electric connections therefrom, and an armature sub-assembly comprising an armature bar of cross sectional shape smaller than said bore and having a length in excess of the distance between said pole plates, an

armature mounting sleeve having an exterior circumference substantially the same as the interior circumference of said bore, a retaining tab secured at one end to the mounting sleeve, the other end of said tab having an arm adapted to overlie the coil'form, a transverse pivot pin on said bar intermediate opposite ends thereof and pivotally mounted in said mounting sleeve, an armature return spring having a saddle in engagement with said bar at a location between said pivot pin and one end of the bar, a leg at the end opposite said saddle having a retained position relative to said tab, a movable electric contact on said bar at a location between said' fixed electric contacts and spaced from one of them, and a flexible connection from said movable contact, said armature mounting sleeve being slideable into said bore from one end thereof whereby to mount said armature sub-assembly in operating position.

3. A micro-miniature electric relay device comprising an hermetically enclosed housing, a magnetic sleeve having a coil form having a bore therethrough, north pole and south pole plates at opposite ends of said coil form and a coil winding around said coil form intermediate said north pole and south pole plates, a pair of fixed electric contacts having fixed positions relative to said coil form, and an armature sub-assembly comprising an armature bar of square cross sectional shape smaller than said bore and having a length in excess of the distance between said pole plates, an armature mounting sleeve having an exterior circumference substantially the same as the interior circumference of said bore, a retaining tab secured at one end to the mounting sleeve, the other end of said tab having an arm adapted to overlie the coil form at one end, a transverse pivot pin on said bar intermediate opposite ends thereof and pivotally mounted in said mounting sleeve, an armature return spring having coils extending around respective ends of said pivot pin, a saddle between said coils in engagement with said bar at a location between said pivot pin and one end of the bar, a leg on at least one of said coils at the end opposite said saddle and having a retained position relative to said other end of the tab, a movable contact on said bar at a location between said fixed electric contacts and spaced from one of them, and a flexible connection from said movable electric contact, said armature mounting sleeve being slideable into said bore from one end thereof whereby to mount said armature sub-assembly in operating position.

4. A micro-miniature electric relay device comprising an hermetically enclosed housing, a magnetic sleeve having north pole and south pole plates at opposite ends, a coil form having a bore therethrough, and a coil winding around said coil form intermediate said north pole and south pole plates, said north pole plate having laterally spaced legs forming an opening facing in one direction and said south pole plate having laterally spaced legs forming an opening facing in the opposite direction, a conductor insulator element having a fixed position relative to said housing at a location intermediate one of said pole plates and a respective end of said housing, a pair of fixed electric contacts on said insulator element having a space therebetween and electric connections therefrom through said end of said housing, and an armature sub-assembly comprising an armature bar of square cross sectional shape smaller than said bore and having a length in excess of the distance between said pole plates, an armature mounting sleeve having an exterior circumference substantially the same as the interior circumference of said bore, a retaining tab secured at one end to the mounting sleeve, the other end of said tab having a transversely extending arm adapted to overlie the coil form at the end opposite said insulator element, a transverse pivot pin on said bar intermediate opposite ends thereof and pivotally mounted in said mounting sleeve, an armature return spring having coils extending around respective ends of said pivot pin, a saddle between said coils in engagement with said bar at a location between said pivot pin and said insulator element, a leg on at least one of said coils at the end opposite said saddle and having a retained position beneath said arm of said tab, a movable electric contact on said bar at a location between said fixed electric contacts and spaced from one of them, and a flexible connection from said movable electric contact through said respective end of said housing, said armature mounting sleeve being slideable into said bore from the end opposite said insulator element whereby to mount said armature sub-assembly in operating position.

5. A micro-miniature electric relay device having a transient voltage suppression construction comprising a coil form having a bore therethrough and parallel axially spaced end elements at the ends of said bore, north pole and south pole plates at opposite ends of said coil form and a coil winding around said coil form intermediate said north pole and south pole plates, a pair of electric contacts having a fixed position relative to said coil form, and an armature sub-assembly comprising an armature bar of cross sectional shape smaller than said bore, an armature mounting sleeve of highly conductive material having an exterior circumference substantially the same as the interior circumference of said bore, retaining means secured respectively to the mounting sleeve and the coil form, means intermediate opposite ends of said bar pivotally mounting said bar in said mounting sleeve, an armature return spring in engagement with said bar at one side of a pivot point and another portion having a retained position relative to said retaining means, a movable electric contact on said bar at a location between said pair of electric contacts and spaced from one of them, and a flexible connection from said movable electric contact, said armature mounting sleeve being slideable into said bore from one end whereby to mount said armature subassembly in operating position, an insulating layer around the exterior of said coil winding, a magnetic sleeve covering said insulating layer and extending into engagement with said pole plates, a suppression sleeve of relatively thin highly conductive material lying between said insulating layer and said magnetic sleeve, said end elements being of highly conductive material and extending into engagement with respective ends of said suppression sleeve.

6. A micro-miniature electric relay device comprising a coil form having a bore therethrough, north pole and south pole plates at opposite ends of said coil form, and a coil winding around said coil form intermediate said north pole and south pole plates, a magnetic sleeve extending between said pole plates over the exterior of said coil winding, and an insulating layer between said magnetic sleeve and said coil winding, a pair of electric contacts having a fixed position relative to said coil form and including respective electric connections therefrom, and an armature sub-assembly comprising an armature bar of cross sectional shape smaller than said bore and having a length in excess of the distance between said pole plates, an armature mounting sleeve of non-magnetic relatively highly conductive material having an exterior circumference substantially the same as the interior circumference of said bore, and a length substantially the same as the length of said bore, retaining means secured between said mounting sleeve and the coil form, a transverse pivot pin on said bar intermediate opposite ends thereof and pivotally mounted in said mounting sleeve, an armature return spring in engagement respectively with said bar, and coil form for tilting said bar and a movable electric contact on said bar at a location between said fixed electric contacts and spaced from one of them, a relatively thin transient suppression sleeve of non-magnetic relatively high conducting material between said insulating layer and said magnetic sleeve and discs of non-magnetic relatively high conducting material underlying said pole plates and eX- tending between said coil form and said suppression sleeve.

References Cited UNITED STATES PATENTS 3/1961 Juptner 200-87 X 4/1966 Sauer 200-87 X 

1. A MICRO-MINIATURE ELECTRIC RELAY DEVICE COMPRISING A COIL FORM HAVING A BORE THERETHROUGH, NORTH POLE AND SOUTH POLE PLATES AT OPPOSITE ENDS OF SAID COIL FORM AND A COIL WINDING AROUND SAID COIL FORM INTERMEDIATE SAID NORTH POLE AND SOUTH POLE PLATES, A PAIR OF ELECTRIC CONTACTS HAVING A FIXED POSITION RELATIVE TO SAID COIL FORM, AND AN ARMATURE SUB-ASSEMBLY COMPRISING AN ARMATURE BAR OF CROSS SECTIONAL SHAPE SMALLER THAN SAID BORE AND HAVING A LENGTH IN EXCESS OF THE DISTANCE BETWEEN SAID POLE PLATES, AN ARMATURE MOUNTING SLEEVE HAVING AN EXTERIOR CIRCUMFERENCE SUBSTANTIALLY THE SAME AS THE INTERIOR CIRCUMFERENCE OF SAID BORE, A RETAINING TAB SECURED AT ONE END TO THE MOUNTING SLEEVE, THE OTHER END OF SAID TAB HAVING AN ARM ADAPTED TO OVERLIE THE COIL FORM, MEANS INTERMEDIATE OPPOSITE ENDS OF SAID BAR PIVOTALLY MOUNTING SAID BAR IN SAID MOUNTING SLEEVE, AN ARMATURE RETURN SPRING HAVING A SADDLE IN ENGAGEMENT WITH SAID BAR AT ONE SIDE OF A PIVOT POINT AND ANOTHER PORTION AT THE END OPPOSITE SAID SADDLE HAVING A RETAINED POSITION RELATIVE TO SAID TAB, A MOVABLE ELECTRIC CONTACT ON SAID BAR AT A LOCATION BETWEEN SAID PAIR OF ELECTRIC CONTACTS AND SPACED FROM ONE OF THEM, AND A FLEXIBLE CONNECTION FROM SAID MOVABLE ELECTRIC CONTACT, SAID ARMATURE MOUNTING SLEEVE BEING SLIDEABLE INTO SAID BORE FROM ONE END WHEREBY TO MOUNT SAID ARMATURE SUB-ASSEMBLY IN OPERATING POSITION. 